This application relates to an improved brake system for a vehicle, particularly one which is subject to significant variable loading, such as a van. The brake system utilizes a proportioning valve between the master cylinder and the rear brakes. Its purpose is to increase the effect of rear braking as the vehicle is loaded. Conversely, the valve decreases the rear braking effect when the vehicle load decreases.
Prior use of a rear brake proportioning valve include the 1984-1985 Chrysler Corporation built T-115 van and wagon, namely the Plymouth "Voyager" and the Dodge "Minivan" and "Caravan." In these vehicles, a proportioning valve is attached to a body cross member slightly forward of the rear axle and slightly to the left of the vehicle center line. A lever assembly is attached to the rear axle rightward of the proportioning valve and projects upward from the axle. An elongated tension-type spring extends between the lever assembly and the proportioning valve. When the vehicle is lightly loaded, the position of the lever end of the tension spring is only slightly higher than the proportioning valve end. As vehicle load increases, the valve end moves further downward with respect to the lever end and, thus, extends the spring resulting in an increased force applied to the proportioning valve. Resultantly, the valve directs increased fluid pressure to the rear brakes for greater rear braking.
The aforedescribed brake system operates satisfactorily. However, the location of the valve, spring and lever assembly is somewhat inconvenient since the spare tire is stored immediately to the rear of these components. It would improve the accessibility of the spare tire if these brake components were placed elsewhere.
It is important to locate the proportioning valve where it is protected. It has been found that a desirable location for the valve is just forward of the rear wheel and up near the forward end portion of the rear leaf-type suspension spring. This is where the forward end of the leaf spring is connected to the vehicle. In this location, the proportioning valve can be supported by the same longitudinal body of chassis member which also supports the spring end. In the position, the input force means for the valve extends directly to a position follower sensing means which is operably connected to the leaf spring end.
The degree of vehicle load in the subject application is sensed by a position follower device which is operably connected to the forward end portion of the rear suspension spring. As the vehicle load increases, the spring's end portion is pivoted through an arc as the vehicle body and spring ends move downward with respect to the spring mid-portion. A projecting arm of the position follower is attached to one end of a spring loaded and axially yieldable connector. The other end of the connector is attached to the input control of the proportioning valve which is force responsive. As the follower pivots due to loading of the vehicle, the force input to the proportioning valve is increased. Resultantly, an increased brake pressure is directed to the rear brakes.
Therefore, an object of the invention is to provide an improved vehicle brake proportioning system which utilizes a load sensing input means operating directly in response to movements of a vehicle rear suspension spring for controlling a proportioning valve.
A further object of the invention is to provide an improved vehicle brake proportioning system, including a rear suspension spring position follower directly engaging the end portion of the rear suspension spring, pivoting with the spring end as the spring responds to increased vehicle loading and transmitting load forces via an axially yieldable and spring biased connector to a proportioning valve.
Other objects and advantages of the subject invention will be readily apparent from a reading of the following detailed description of the preferred embodiment, which is shown in the following drawings.